JPS6335082B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heating resistor for a hot wire flowmeter suitable for detecting the intake air flow rate of an internal combustion engine, for example.

Conventionally, a heating resistor for a hot wire flowmeter has a structure in which a thin platinum wire is wound around an alumina pipe hobbin having leads at both ends. However, since there is no winding device on the market that can evenly wind thin wires with a diameter of 50μ or less, the winding work had to be made in-house, and a device integrated with a terminal spot welding device was developed to match the production volume. I needed to go. Furthermore, since the winding wire is made of thin platinum wire, the inner diameter of the base for positioning the winding wire is abnormally small, and even if it is made of carbide, it wears heavily and requires frequent replacement.

On the other hand, thin platinum wire is made from a diameter of 6μ by drawing a die more than 60 times, so most of the cost is processing costs. Therefore, it was necessary to have a cost structure that was close to the material cost for a material weighing 3 mg, so a method was devised to form a thick platinum film on the surface of the alumina pipe hobbin.

The thick film is formed by dipping the bobbin in a platinum thick film paste stirred solution containing a binder in advance, drying and baking, and trimming the deposited platinum thick film layer in a spiral shape with a laser to obtain the required resistance value. . Let this sample self-heat to 300℃ and turn on the power for 4 seconds.
If you continue the cycle test of ON, 4 seconds OFF, 5
After 10,000 cycles, the change in output voltage V ₀ (V) with respect to flow rate Q (Kg/H) is 15% in terms of ΔQ/Q.
It turns out that this is all. However, as a flow meter, the change before and after the 100,000 km driving durability test of a car is ±
The permissible value is 3% or less.

The reason for this change is the difference in expansion coefficients between the thick platinum film and alumina joint (7.7×10 ^-6 for alumina and 8.9×10 ^-6 for platinum), which weakens the bonding force and causes internal strain in the platinum particles. It is thought that this promotes the change in resistance value. In addition, the platinum thick film is 10μ to 20μ
Although a thick film is deposited on the platinum layer, a dense film is not obtained after firing, and cracks appear in the platinum layer, allowing current to flow through the bridge path from land to land. It is thought that such cracks change due to the expansion and contraction of platinum itself due to changes in temperature, and the movement of ions due to the flow of current is considered to be a cause of even more subtle changes over time.

Furthermore, when trimming a resistor using a laser, the energy of the laser that hits the thick film resistor reaches the alumina surface and forms a groove in the alumina, reducing its strength to the extent that it cannot withstand the vibration load of the bobbin reaching 60G. It was causing a problem.

An object of the present invention is to provide a heating resistor for a hot-wire flowmeter that requires fewer processing steps, is inexpensive, has little change over time as a flow rate sensor element, and has sufficient resistance to external mechanical forces such as vibrations. .

The present invention will be explained in detail below. The bonding strength between the alumina pipe and the resistor formed on its surface is improved by the metallized layer, and the resistor is formed on the metallized layer to improve the adhesion between each bonding material and form a dense resistor. Obtain a membrane. The optimal conditions for metallization between the ceramic and the material to be bonded are such that the coefficients of thermal expansion are approximately similar to each other, and the metallized material has a larger compressive force within about 10%, which constantly applies compressive force to the ceramic. desirable. The reason for this is that the compressive strength of ceramics is generally about 10 times higher than its tensile strength. Next, ceramics are not limited to alumina, but also have good wettability with metallizing materials.
It is best to select and combine materials that are compatible with each other.
In this way, the diffusion of these materials at the joint is promoted and the joint strength is improved.

The metallizing material is a metal oxide or an inorganic material. The electrical resistance of the metallizing material is made large, and the resistor is deposited on the metallizing material to obtain a dense and stable resistance layer. In this case, the metallizing layer absorbs excess laser energy during laser cutting of only the resistor layer and serves as a protective wall to prevent harmful damage to the ceramic. The resistor can be selected based on the optimal bonding conditions with the metallizing material, such as platinum, which has a relatively small temperature coefficient and expansion coefficient, and Ni, Cu, which has a relatively large coefficient of expansion. Platinum is chemically stable.

On the other hand, it is necessary to work in a reducing atmosphere or an inert gas atmosphere to prevent the resistor from oxidizing, but Ni and Cu are advantageous in that they are relatively inexpensive and have a large temperature coefficient.

Ceramic base materials include magnesia, holsterite, beryllia, and
Steatite, alumina, zirconia, spinel, mullite, etc. are listed, and metallizing materials include FeNiCu alloy, Nb, Ti, Ta, Mo, W, etc., but bonding requires metal oxidation, wetting, adsorption, diffusion, etc. Since complex processes are involved, it is necessary to select and combine them in consideration of their compatibility.

There is a high melting point metal method as a metallizing treatment method. The metallizing composition includes Mo, MoO ₃ ,
W, WO ₃ , Mo―Mn, Mo―Mn―Ti, Mo―
SiO ₂ , Mo―MoO ₂ ―TiO ₂ , MoO ₂ ―Mn―Ti,
Mo―SiO ₂ , W―MnO ₂ ―TiO ₂ ―SiO ₂ , W―Re―
Examples include MnO ₂ -TiO ₂ . To explain an example of the metallizing bonding mechanism, in the humidified forming gas during metallizing, a part of Mn in the metallizing layer, especially the surface, becomes MnO by the following reaction.

Mn + H ₂ O → MnO + H _2This MnO comes into contact with the glass phase in the alumina ceramics and dissolves into it. The glass phase becomes more fluid and enters the voids in the metallizing layer where sintering is progressing, bonding the alumina ceramics and the metallizing layer. Also at the same time
MnO reacts with Al ₂ O ₃ to form MnO.Al ₂ O ₃ and becomes an intermediate layer. The surfaces of Mo and Mn are slightly oxidized in the humidifying gas forming gas, and are well wetted by the glass phase.
The oxides on the Mo and Mn surfaces dissolve into the invading glass phase and form a complete bond. Furthermore, a film of Ni is deposited as a resistor by chemical plating, etc., and when cured, the heating temperature during curing causes Ni to interdiffuse with Mo and Mn into the voids of the metallizing layer that still remain, resulting in complete bonding. Metallizing can be performed by vacuum processing methods such as vapor deposition, ion plating, and sputtering. For example, before metallizing, the surface of ceramics is polished with diamond powder, and then washed with water.
Clean by air baking at 1000℃.

Furthermore, it is then cleaned by plasma arc treatment. This ceramic material is placed in a vacuum of 5×10 ^-6 Torr or less, and the ceramic substrate is heated to 500 to 1000° C. in a resistance furnace. Mo on top of that
Deposit about 10μm. It is also possible to form a resistor by plating Ni or the like on the metallized ceramics, or to join a metal resistor through a metal brazing material. The next metallizing treatment method is thermal spraying. Flame spraying method, depending on the mechanism of thermal spraying.
There are plasma spraying methods, explosion spraying methods, line explosion spraying methods, etc., which involve melting metals, oxides, carbides, silicides, etc. and spraying them onto a substrate to form a uniform film. There is also a method of using metal solder or oxide solder. In the method using metal solder, various types of metal solder are sandwiched between ceramics and metal, and heated in air, inert gas, reducing atmosphere, or vacuum to melt and bond the metal solder. Metal solders include (1) indium and indium alloys (2) aluminum (3) Pb-Sn-Zn-Sb alloys (4) Ti-Ni, Ti-Cu, Zr-Ni, and Zr-Cu.

To explain (4) in detail here, Ni and Cu, which form alloys with relatively low melting points such as Ti and Zr, are inserted between the ceramic and the metal, and heated once in vacuum or inert gas. Combine by operation.
These hydrogen compounds TiH, instead of Ti and Zn,
ZrH etc. may also be used. When joining alumina and Ni using Ti--Ni solder, the following process is considered to occur. During heating during the bonding operation, Ti and Ni gather near the interface between the solder and alumina, and as shown in Figure 1, Ti is selectively absorbed on the alumina side. Figure 1 is an elemental analysis diagram obtained by XMA analysis of Ni attached to alumina using Ti-Ni solder. This Ti diffuses into alumina and reacts. In particular, SiO ₂ contained in a small amount in alumina ceramics and Ti react to form SiO ₂
is reduced, and TiO ₂ , TiO, Ti ₂ O ₂ , etc. are generated. Ti, Si, and their oxides diffuse and react with each other to form an intermediate layer at the interface, forming an airtight and mechanically stable bonded body. This is a method in which an oxide is used as a solder, and the solder is similarly inserted between ceramics and metal, and the solder is heated and bonded. If the atmosphere during bonding is high temperature,
It is carried out in an inert, reducing atmosphere or vacuum to prevent overoxidation of the sealing metal. Oxide solders are classified according to whether they are amorphous or crystalline after bonding, but CaO
―Al ₂ O ₃ ―MgO―B ₂ O ₃ system, CaO―Al ₂ O ₃ ―MgO
- Examples include SiO ₂ series. Bonding using these solders is ideal for metallizing plate-shaped ceramics. Note that FIG. 2 shows an elemental analysis diagram obtained by analyzing by XMA a state in which Nb is deposited and bonded to alumina via oxide solder.

An embodiment of the present invention will be described below.

Metal leads 5 are attached to both ends of a ceramic pipe 1 as shown in FIG. 3a, a ceramic plate 2 as shown in FIG. 3b, or a ceramic rod 3 as shown in FIG. After metallizing alloys and metal oxides to ceramics, they are firmly bonded through a plating layer or brazing material. In this case, as shown in FIG. 4, the ceramic material is metallized as a preliminary treatment to firmly attach the resistor 10, so the ceramic material has a wettability similar to that of the metallized material 8 in terms of expansion coefficient. Selected based on quality. Here, alumina was used as the ceramic material. The expansion coefficient of alumina is 7.7×10 ^-6
(1/°C). Metallizing material 8 is Mo
- It is formed by mixing Mn with an organic binder to form a paint, applying this to the surface of ceramics, and metallizing it at a temperature of 1000 to 1500°C in hydrogen gas, inert gas, or a mixture of these gases. In the humidified forming gas during metallizing, some of the Mn in the metallizing layer is
It becomes MnO. This MnO comes into contact with the glass phase in the alumina, dissolves therein, enters the voids in the metallizing layer, and joins the alumina and the metallizing layer. MnO reacts with Al ₂ O ₃ to form an intermediate layer MnO・
Al ₂ O ₃ is formed. Furthermore, the resistor is formed by plating with Ni. Alternatively, it is formed by depositing a Cu film. Ni and Cu enter the voids in the metallizing layer that remain during heat treatment after plating or during Cu brazing.
It interdiffuses with Mo and Mn to form a perfect bond. Ni
is a resistor and has a temperature coefficient of 6700 ppm/°C, making it possible to obtain high sensitivity.

Here, the case where copper oxide method is used as metallization will be explained. Powders with a composition of 94.2% CuO and 5.8% Al ₂ O ₃ are mixed, heated in air at 1250°C for 30 minutes, cooled, and then pulverized. This is applied to the ceramic surface by spraying or dipping. The copper is then metallized by heating to a melting point of 1190° C. or above of the coating material, and then to about 1000° C. in a reducing atmosphere. In the metal soldering method, active metals Ti, Ni, or Cu are formed on ceramics by vapor deposition in advance, and a sheet of Ni or CCu as a resistor is applied to this and heated at 1000 to 1500°C in an inert gas, such as Ar gas. Join.

In the oxide soldering method, for example, CaO―Al ₂ O ₃ ―
Oxide solders such as MgO-based and CaO-Al ₂ O ₃ -MgO-SiO-based are used as highly heat-resistant crystalline solders, and these solders are placed directly between ceramics and metal and heat-treated to bond them. . This method is relatively simple in the case of sheets, but
When metalizing the outer periphery of a cylinder or rod, a method is used in which a metallizing material is deposited in advance by vapor deposition or sputtering.

Examples of metallizing methods include cleaning the ceramic surface in advance as described above, heating it in a vacuum, and depositing a metallized layer by vapor deposition, sputtering, ion plating, etc., and thermal spraying.

After metallizing such ceramics, the resistor is bonded, the resistor is trimmed by a laser or the like, and a glass coating 15 is applied to the surface of the resistor to prevent deterioration over time.

According to the embodiment described above, the following effects can be obtained.

(1) Since the resistor can be bonded to ceramics through a metallized layer, the bonding strength is improved, and the flow sensor element has high accuracy and withstands self-heating to 300℃, ON4sec, OFF4sec thermal cycle tests, and has little change over time. is obtained. Figure 5 shows experimental data that proves this effect.
The metallized product that connects the white circles has a significantly improved accuracy compared to the non-metalized product that connects the black circles, and has a flow rate of 8 to 320 kg/h (1 to 40 kg/h).
m/s), the change over time can be suppressed to ±3% or less.

(2) Inexpensive materials such as Cu and Ni can be used as resistor materials, reducing costs.

(3) As a resistor, it has a very large temperature coefficient.
6700ppm/℃Ni material can be selected, improving the sensitivity of the flowmeter.

(4) It can be processed sufficiently using ready-made equipment, and productivity can be improved.

As is clear from the above description, the heating resistor for a hot-wire flowmeter according to the present invention requires fewer processing steps, is inexpensive, has little change over time as a flow sensor element, and is not susceptible to mechanical external forces such as vibrations. be able to withstand enough.

[Brief explanation of the drawing]

Figure 1 shows Ni solder applied to alumina using Ti-Ni solder.
Figure 2 is an elemental analysis diagram analyzed by XMA with Nb bonded to alumina via oxide solder.
Figures 3a, b, and c are configuration diagrams showing embodiments of the present invention, and are cross-sectional views of each flow rate sensor element. Figure 4 is an enlarged cross-sectional view showing the state of film bonding of the flow rate sensor element. Figure 5 is a flow rate sensor element. It is a graph showing a change in a sensor element over time. 1... Ceramic pipe, 2... Ceramic plate, 3... Ceramic rod, 5... Metal lead, 1
0...Resistor, 8...Metallizing material, 15
...Glass coat.

Claims (1)

[Claims] 1. In the configuration of a heating resistor that is formed by forming a laser-trimmed resistor on the outer peripheral surface of a ceramic with leads fixed at both ends and used as a sensor element of a flowmeter, the outer peripheral surface of the ceramic is made of Ni or Cu. The resistor is made of Mo―Mn
A heating resistor for a hot wire flowmeter, characterized in that it is formed with a metallized layer interposed therebetween.